1. Field of the Invention
The present invention relates to a radio frequency switch circuit for reducing an influence of a deviation voltage of a switching control signal.
2. Description of the Related Art
In general, a semiconductor integrated circuit installed in a wireless communications device such as a cellular phone includes a radio frequency semiconductor switch (hereinafter, referred to as a radio frequency switch circuit) for controlling a transfer path of a high frequency signal between an antenna and a transmitting/receiving circuit.
Such a radio frequency switch circuit requires low loss, high isolation, and a high switching speed, and also requires low harmonic distortion, that is, high linearity, even in the case that a large signal is input.
In a basic wireless communication device, a radio frequency switch circuit includes a plurality of radio frequency ports that are connected to a plurality of transmitting/receiving circuits, respectively, and a common port connected to an antenna.
The radio frequency switch circuit controls a transfer path of a high frequency signal between the radio frequency ports and the common port such that one is selected from among the transmitting/receiving circuits connected to the radio frequency switch circuit and is electrically connected to the antenna.
Such an existing radio frequency switch circuit includes a switch transistor connected between each radio frequency port and the common port, and a shunt transistor connected between each radio frequency port and a ground in order to convert a transfer path of the high frequency signal between each radio frequency port and the common port.
In this case, each of the switch transistor and the shunt transistor may be a switch device on a silicon on insulator (SOI) substrate and may be a metal oxide silicon field effect transistor (MOSFET).
In such an existing radio frequency switch circuit, a switching control signal for controlling in an on-state or an off-state is supplied to a plurality of switches and a gate of each shunt transistor. The switching control signal may be supplied from a base band chipset.
However, the switching control signal supplied to the switch and shunt transistor included in the radio frequency switch circuit may not have a required voltage level and may have a deviation voltage that is different from the required voltage level. When the switching control signal has the deviation voltage, the deviation voltage may not be compensated for, thereby degrading switch properties.
For example, when a turn-on voltage of the shunt transistor is 0.45 V, in a case in which the control signal having a deviation voltage not 0 V is supplied to the gate of the shunt transistor as a low level for turn-off, the shunt transistor needs to be turned off. However, when a voltage (e.g., 0.3 V) that is lower than the turn-on voltage and equal to or higher than a sub_threshold voltage is applied to the gate, the shunt transistor may be slightly turned on.
Accordingly, loss of the radio frequency signal comes from the shunt transistor, thereby causing deterioration in return loss or harmonic characteristics in the radio frequency switch circuit.
The Related Art Document below discloses a radio frequency switch circuit and a semiconductor device but does not disclose technical features related to reducing the influence of a deviation voltage of a switching control signal.